Variable-frequency interdigital magnetron



#54721? SUPPLY BIAS 4ND MODULA TING R mm F- M 6 V m 4 W v m 1 H Filed Dec. 9, 1949 /ZOJjW ATTORNEY netron along the line 22 side cathode lead whereas fingers Patented Dec. 11, 1951 VARIABLE-FREQUENCY INTERDIGITAL MAGNETRON Henry J. McCarthy,

Sylvania Electric of Massachusetts Danvers, Products Masa, minor to Inc., a corporation Application December 9, 1949, Serial No. 132,004

Claims.

The present invention relates to electronically tunable magnetrons of the interdigital type and to such magnetrons in frequency-modulation circuits.

This type of magnetron commonly includes a cylindrical array of axially extending anode conductors encircling a cathode, the anode conductors being separated into sets with the conductors of each customarily occurring in alternation with those of the other. The sets are connected to a frequency-controlling device .that may be a lecher wire system but commonly takes the form of a cavity resonator, and this is conveniently formed as a metallic envelope and is evacuated. This form of magnetron has many attractive features, and the object of the present invention is to adapt it to effective variable-frequency operation in a simple manner, particularly to improve its construction and to provide auxiliary circuit connections enabling rapid electronic tuning and modulation of the operating frequency.

In my illustrative embodiment described below, the usual magnetron having the two cylindrical sets of interdigital anode fingers about a cathode is equipped with an additional cathode outside the usual electron-discharge space, and constituting with the usual anode conductors a kind of inside-out secondary magnetron. The nature of the invention, and further features of novelty and explanation appear in the following detailed description of an illustrative embodiment shown in the accompanying drawings, wherein:

Fig. 1 is an axial cross-section of an interdigital magnetron and certain circuit connections embodying features of my invention; and

Fig. 2 is a transverse cross-section of the magin Fig. 1.

In the drawin main cathode l0 having electron-emissive coating l2 and coiled heater I4 is supported coaxially within a cylindrical array of axially extending fingers or anode conductors Na and l6b. The physical support of the oathode is in a glass seal (not shown) centering out- |8 within bore 20 of pole-piece 22 of magnetic material. Inner conductor 24 of the cathode heater is likewise hermetically sealed within conductor l8. Anode fingers |6a are supported by conductive end wall 25a of the cavity resonator which interconnects those fingers, l6b are similarly supported and electrical interconnected by conductive end wall 261) of the cavity resonator. Cylindrical outside wall 26c completes the resonator, which here also forms most of the envelope about the main electron-discharge space between anode l6a, I 6!) and cathode I. As is known, a separate resonator can be supported outside an evacuated glass envelope enclosing the electron-discharge electrodes. A second pole-piece 28 01' soft iron or the like, opposite pole-piece 22, directs a strong magnetic field axially along cathode l0, between the cathode and the encircling anode fingers, and to a limited extent outside those fingers. A magnet (not shown) is mounted in contact with pole-pieces 22 to pro ide the required magnetic field. Output coupling loop 30 and coaxial leads 32 complete a known form of interdigital magnetron. A seal (not shown) is formed about lead 32 to enable evacuation of the cavity resonator.

The usual interdigital magnetron is conceived to operate by establishing a spoked wheel of the cloud of electrons in the space between cathode Ill and anode lGa-I 6b, which wheel induces voltages in the anode fingers. An electron spoke is attracted toward the next anode finger that is positive. One set of anode fingers is positive at an instant that the other alternate set is negative, and there are half the number of spokes as anode fingers in this interdigital magnetron. The fingers, connected to the resonator ends, energize the resonator and are in turn energized by it. Each time the spoked wheel advances the space of one anode finger, the resonator excitation passes through one half a cycle, and the spoked electron wheel is caused to advance one anode finger for each half-cycle of the resonator.

In order to adjust the operating frequency the resonator has heretofore been madeadjustable mechanically. In accordance with the present invention, a second or additional cathode 34 is provided, positioned outside the discharge space of the main or primary cathode. This cathode has an electron emissive surface 36 and a heater 38 having coaxial leads 40, 42 hermetically sealed to each other and to the outer tube 44 extending from the resonator. A biasing and irequency-controlling voltage supply or modulator 46 is connected between cathode 34 and the resonator. Cathode 34 is heated by supply 48. Cathode 34 extends across or spans multiple anode fingers including one from each end wall 26a, 26b of the resonator, although it could be extended about more if not all of the anode fingers with due regard for mechanical support, insulation, and the electromagnetic field in the resonator.

Anode fingers l6a, lib can be visualized as functioning with cathode N as an inside-out magnetron in accordance with all the usual principles, but in this instance it is energized to operate below'the level of self-oscillation even were its geometry otherwise suited to self-oscillation. This secondary magnetron tends to establish moving electron spokes. but these tend to move slower than the primary electron wheel. By bringing the secondary oscillator closer to operation by virtue of changed appliedvoltage, the primaryelectron cloud is permitted to advance faster, 'nioreinearly at its speed in the absence of cathode ll. This possible explanation can be verified by reactance measurements of magnetrons below oscillation levels. The voltage from supply can be changed slowly for frequency control, or supply 48 can be constructed to yield a modulating signal and to eifect frequency-modulation.

While an illustrative embodiment and its underlying principles have been described, variations in detail and changed arrangements will occur to those skilled in the art. Therefore, it is appropriate that the appended claims be given that latitude interpretation that accords with the spirit and scope of the invention.

WhatIclaim is:

1. A magnetron device of the interdigital type adapted to be electronically controlled in oscillation frequency, including a multipart anode assembly having acylindrical array of conductors interconnected at their ends into two anode portions, the conductors of each portion extending between the conductors of the other portion, a cathode positioned within the cylindrical array of anode conductors, and an additional cathode extending across plural anode conductors outside said cylindrical array of conductors.

2. A magnetron device of the interdigital type adapted to be electronically controlled in oscillation frequency, including a multipart anode assembly including two substantially parallel conductors, two sets of anode fingers extending in a cylindrical array from each of said parallel conductors toward the other of said parallel conductors, the fingers of each set extending between the fingers of the other set, a cathode within said cylindrical array of anode fingers, and an additional cathode spanning multiple anode fingers outside the cylindrical array.

3. A magnetron device adapted to be electronically controlled in operating frequency, including two sets of anode conductors arranged in alternation in a cylindrical array, primary cathode means providing an electron cloud within said cylindrical array, and control cathode means spanning multiple anode fingers outside said cylindrical array.

4. A magnetron device adapted to be electronically controlled in operating frequency, including an envelope, a cylindrical array of axially extending conductors interconnected in alternation, a main cathode providing a primary electron cloud within said cylindrical array, and an additional cathode outside said cylindrical array forming an electron discharge space to plural anode conductors.

5. A magnetron device adapted to be electronically controlled in operatingfrequency, including a central cathode, a cylindrical array of anode conductors extending substantially axially, a cavity resonator having end portions connected, respectively, to alternate ones of said anode conductors and an additional cathode outside said cylindrical array of anode conductors and inside said resonator.

6. A magnetron device adapted to be electronically controlled in operating frequency including an interdigital cylindrical anode assembly having two sets of axially extending fingers arranged in alternation, a cathode providing an electron discharge space within said cylindrical anode assembly, a cavity resonator interconnecting and enclosing said sets of anode fingers, an additional cathode outside said cylindrical array but inside said resonator, and means providing frequency control voltage between said anode assembly and said additional cathode.

7. A frequency-modulated magnetron having a main cathode, an enclosing cavity resonator, a cylindrical array of axially extending fingers supported in alternation from the ends of said resonator about said primary cathode, an additional cathode spanning multiple anode fingers including at least one finger supported by each end of the cavity resonator, and modulating voltage supply means connected between said additional cathode and said resonator.

8. A magnetron device of the interdigital type adapted to be electronically controlled in oscillation frequency, including a cylindrical array of axially extending anode fingers alternate ones of which are interconnected by one circular conductor, the remaining fingers being interconnected by another circular conductor, a cavity resonator encircling said axially extending conductors, the ends of said cavity resonator being in part constituted of said circular conductors respectively, a primary cathode encircled by said fingers and a secondary cathode spanning a multiplicity of said fingers outside said cylindrical array, said secondary cathode and said spanned fingers constituting a supplemental magnetron whose operation affects the frequency of the primary cathode, the axially extending anode fingers and said resonator.

9. A magnetron device including a primary interdigital magnetron having a primary cathode and a cylindrical set of interdigitated anode fingers coaxial with said cathode, said fingers being connected to a cavity resonator, and a secondary interdigital magnetron having a supplemental cathode spamiing multiple ones of said anode fingers on the side thereof opposite said primary cathode, the phase of said secondary interdigital magnetron being effective to modify the operating frequency of the primary interdigital magnetron.

10. A magnetron including a pair of interdigital magnetron portions having separate cathodes but employing an interdigital anode assembly and a resonator in common, said anode assembly including a cylindrical array of fingers, and each of said cathodes extending opposite of a plurality of said fingers.

HENRY J. McCARTHY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,421,636 McArthur et al June 3, 1947 2,446,531 Derby Aug. 10, 1948 2,475,646 Spencer July 12, 1949 FOREIGN PATENTS Number Country Date 615,034 Great Britain Dec. 31, 1948 

